# Constant Current Load

**Libraries:**

Simscape /
Electrical /
Passive

## Description

The Constant Current Load block implements a constant current load for a DC or AC supply.

If you set the **Load type** parameter to
`DC`

:

The consumed current of this block is equal to the value of the

**Consumed current**parameter as long as the voltage from the DC supply is equal to or greater than the value specified for the**Minimum supply voltage**parameter.When the voltage from the DC supply drops below

**Minimum supply voltage**, the load behaviour changes and the block models a resistive load. If the supply voltage becomes negative, the block models a small open-circuit conductance.

To ensure smooth transitions between these behaviours, the block uses a third-order
polynomial spline with continuous derivatives. You can specify the width of this
transition using the **Transition voltage width** parameter.

If you set the **Load type** parameter to `AC`

:

The root mean square consumed current of this block is equal to the value of the

**Consumed current (RMS)**parameter as long as the voltage from the AC supply is equal to or greater than the value specified for the**Minimum supply voltage (RMS)**parameter.When the voltage from the AC supply drops below the

**Minimum supply voltage (RMS)**parameter, the load behaviour changes and the block models a load with constant resistance.

### Equations

If you set the **Load type** parameter to
`AC`

, the block calculates the peak voltage,
*V _{pk}*, through harmonic
approximation of the instantaneous voltage by using a one-period-integrated Fourier
transform:

$$\begin{array}{l}\mathrm{Re}={f}_{0}{\displaystyle \int v\text{\hspace{0.17em}}sin\left(2\pi {f}_{0}t\right)}\\ \mathrm{Im}={f}_{0}{\displaystyle \int v\text{\hspace{0.17em}}sin\left(2\pi {f}_{0}t+\frac{\pi}{2}\right)}\\ {V}_{pk}=2\sqrt{{\mathrm{Re}}^{2}+I{m}^{2}}\end{array}$$

During the first period, the peak voltage is equal to `0`

`V`

. The current is defined by this equation:

$$i(t)=\frac{V(t)}{{R}_{equiv}},$$

where *R _{equiv}* is the
equivalent resistance and depends on the value of the

**Minimum supply voltage (RMS)**parameter.

If the voltage from the three-phase supply is greater than the value specified for the
**Minimum supply voltage (RMS)** parameter, the equivalent
resistance is defined by:

$${R}_{equiv}=\frac{\frac{{V}_{pk}}{\sqrt{2}}}{{I}_{RMS}{}_{consumed}},$$

where *V _{pk}* is the
voltage peak magnitude and

*I*is the value of the

_{RMSconsumed}**Consumed current (RMS)**parameter.

If the voltage from the three-phase supply is less than the value specified for the
**Minimum supply voltage (RMS)** parameter, the equivalent
resistance is defined by:

$${R}_{equiv}=\frac{{V}_{RMS}{}_{min}}{{I}_{RMS}{}_{consumed}},$$

where
*V _{RMSmin}* is
the value of the

**Minimum supply voltage (RMS)**parameter.

### Faults

To model a fault in the Constant Current Load block, in the
**Faults** section, click the **Add fault** hyperlink in
the parameter that corresponds to the specific fault that you want to model. When the
**Create Fault** window opens, you use it to specify the fault properties.
For more information about fault modeling, see Fault Behavior Modeling and Fault Triggering.

The Constant Current Load block allows you to model an electrical fault as an open circuit. The block can trigger fault events either:

At a specific time

When a power limit is exceeded for longer than a specific time interval

### Load-Flow Analysis

If the block is in a network that is compatible with the frequency-time simulation mode, you can perform a load-flow analysis on the network. A load-flow analysis provides steady-state values that you can use to initialize a machine.

For more information, see Perform a Load-Flow Analysis Using Simscape Electrical and Frequency and Time Simulation Mode.

## Ports

### Conserving

## Parameters

## Extended Capabilities

## Version History

**Introduced in R2021a**